「なに、アンタ疑ってんの」「だ、だってそんな、いきなり魔界とか魔族とか、信じろという方がおかしいよ」

「、」「、、、」

'What, you're doubting me?' 'B-but come on, out of nowhere with demon realms and demon tribes — it's weird to expect me to believe that!'

Literal

'What, you doubting [question-の]?' 'B-but such, suddenly demon-realm [or-とか] demon-tribe [or-とか], believe [quotative-という] side [subject-が] strange [emphatic-よ]'

魔界 'demon realm' and 魔族 'demon tribe' — fantasy terminology. 信じろという方がおかしい uses a sharp rhetorical reversal: 'the one telling me to believe is the strange one.' いきなり 'suddenly, out of nowhere.' The stuttered だ、だって shows flustered resistance. Classic fantasy comedy dialogue.